It is known in the art to include an oxygen scavenger in the packaging structure for the protection of oxygen sensitive materials. Such scavengers are believed to react with oxygen that is trapped in the package or that permeates from outside of the package, thus extending to life of package contents. These packages include films, bottles, containers, and the like. Food, beverages (such as beer and fruit juices), cosmetics, medicines, and the like are particularly sensitive to oxygen exposure and require high barrier properties to oxygen to preserve the freshness of the package contents and avoid changes in flavor, texture and color.
Use of certain polyamides in combination with a transition metal is known to be useful as the oxygen scavenging material. One particularly useful polyamide is MXD6 which contains meta-xylene residues in the polymer chain. See, for example, U.S. Pat. Nos. 5,639,815; 5,049,624; and 5,021,515.
Other oxygen scavengers include potassium sulfite (U.S. Pat. No. 4,536,409), unsaturated hydrocarbons (U.S. Pat. No. 5,211,875), and ascorbic acid derivatives (U.S. Pat. No. 5,075,362).
In barrier layers of packaging walls that are made from blends of oxygen scavenging materials with base polymer resins such as PET haze can result due to such factors as: the immiscibility of the scavenging materials with the base polymer resins, and the inability to create by mechanical blending means disperse-phase domains that are so small as not to interfere with the passage of light therethrough; and the adverse influence of the scavenging material on the crystallization behavior of PET base resin. One approach to minimizing such haze is careful selection of base resin to improve dispersibility of the scavenger material and, thus, reduce, but not substantially eliminate, haze; and to minimize the adverse crystallization effect. This approach may undesirably narrowly restrict the choice of base polymer resin. Another approach is to use compositions that serve as compatibilizers to reduce haze. These approaches add cost to the layer and the compatibilizer adds an additional material that must be evaluated for its suitability for contact with food. There is a need in the art for barrier materials which provide high oxygen scavenging capability and are substantially transparent without use of the aforementioned measures.